Option Explicit

Private Declare Function WaitForSingleObject Lib "kernel32" _
            (ByVal hHandle As Long, _
            ByVal dwMilliseconds As Long) As Long

         Private Declare Function FindWindow Lib "user32" _
            Alias "FindWindowA" _
            (ByVal lpClassName As String, _
            ByVal lpWindowName As String) As Long

         Private Declare Function PostMessage Lib "user32" _
            Alias "PostMessageA" _
            (ByVal hwnd As Long, _
            ByVal wMsg As Long, _
            ByVal wParam As Long, _
            ByVal lParam As Long) As Long

         Private Declare Function IsWindow Lib "user32" _
            (ByVal hwnd As Long) As Long

         'Constants used by the API functions
         Const WM_CLOSE = &H10
         Const INFINITE = &HFFFFFFFF

         Private Sub Form_Load()
            Command1.Caption = "Start the Calculator"
            Command2.Caption = "Close the Calculator"
         End Sub

         Private Sub Command1_Click()
         'Starts the Windows Calculator
            Shell "calc.exe", vbNormalNoFocus
         End Sub

         Private Sub Command2_Click()
         'Closes the Windows Calculator
            Dim hWindow As Long
            Dim lngResult As Long
            Dim lngReturnValue As Long

            hWindow = FindWindow(vbNullString, "Calculator")
            lngReturnValue = PostMessage(hWindow, WM_CLOSE, vbNull, vbNull)
            lngResult = WaitForSingleObject(hWindow, INFINITE)

            'Does the handle still exist?
            DoEvents
            hWindow = FindWindow(vbNullString, "Calculator")
            If IsWindow(hWindow) = 1 Then
               'The handle still exists. Use the TerminateProcess function
               'to close all related processes to this handle. See the
               'article for more information.
               MsgBox "Handle still exists."
            Else
               'Handle does not exist.
               MsgBox "Program closed."
            End If
         End Sub